Using AMD CPU’s in vSphere Hosts
/AMD CPU's offer much greater core density than Intel CPU's and are increasingly gaining market share, due in no small part due to Spectre and associated exploits present in the Intel CPU chipset that do not affect AMD’s chips.
A question that has arisen recently from a customer planning a VDI host refresh was “Can we use AMD CPU's in our replacement VDI hosts?”
It's a good question, historically I have always shied away from using AMD CPU's mainly due to Intel being a trusted vendor and when it comes to what is supported then Intel CPUs are a no-brainer whereas AMD have been a bit of an unknown.
As you will see from my investigations below this is still the case in part but it's definitely changing and I expect that AMD are going to increasingly become a significant player.
Host compatibility
As I base almost all of my VSI and VDI architectures on Dell PowerEdge rack-mount hardware, that's all I am considering for the purposes of this exercise but hopefully the rationale below will give you a framework of what to look for if you are investigating your own preferred hardware platforms for suitability.
Dell PowerEdge servers and AMD CPU's
Dell have a number of different rack-mount servers available for AMD CPU's, these are typically divided into 2 categories, 1 socket and 2 socket:
1 Socket Rack Mount Server
2 socket rack-mount servers
Since the majority of the designs I create are based on the Dell R64x or R74x series servers this is a good start for me - I have server hardware to work with.
nVidia vGPU and AMD
First and foremost nVidia's vGPU technology is compatible with AMD CPUs - although it is definitely worth verifying the specific CPU models you are selecting specifically prior to purchase.
nVidia has some base recommendations in this document.
We now need to consider the server hardware that is certified for GRID vGPU cards, again we're only considering Dell hardware here, the only AMD server certified is the R7425 at the time of writing - but still good news that we have a GRID compatible server.
VMware vSAN compatibility with AMD CPU's
The final aspect for the purposes of my design is compatibility with VMware vSAN - I endeavour to use host hardware based upon vSAN Ready Node specifications from Dell, this ensures that the components that need to be vSAN compatible are indeed vSAN compatible.
More often than not I will customise the specifications and use different (but still compatible) components - such as uprated CPU's - in my designs, but ensuring that the complexities of vSAN and the numerous hardware components and all fully interoperable is essential to ensure my customers do not end up in the nightmare scenario of having a serious failure or problem with a platform that is not a supported hardware configuration.
First the good news, according to this article by Biswapati Bhattacharjee then a vSAN Ready Node configuration for the R7425 exists… happy days.
However, at this point this is where I ran into a bit of trouble since the only vSAN Ready Node configuration that seems to be available in my sizing tool is for a R6415 host – this isn’t GRID compatible and only has a single CPU so not great for getting good user density per host.
I currently have a query open with Dell to determine whether I can get an R7425 Ready Node with the specifications I need.
Other Considerations
Downtime
Switching from Intel CPU-based hosts to AMD CPU-based hosts will require the virtual machines to be powered down prior to migration, since the underlying CPU hardware is changing, the associated virtual machine drivers are different – so be aware that the virtual workloads will need to be shut down prior to host migration.
Speed and Latency
Comparing the speed of the current equivalent Intel and AMD CPU’s they are very much on par for the most part, this article from PC Gamer is worth a read for a more in depth explanation.
Bear in mind that the CPU’s under scrutiny in the article are for mobile and desktop systems – not servers - but parallels will apply since the underlying chip architectures are very similar.
The main difference that the article discusses is the higher cache and memory latency that is present in AMD CPU’s – in standard server virtual workloads this is likely neither here nor there. In very intensive workloads such as CAD applications delivered by VDI or in HPC scenarios however, this latency may prove to let the AMD chip down.
The only way to truly determine whether the latency would be an issue for your specific workload is to run tests against demo or loan hardware before you take the plunge and replace your entire host hardware estate with AMD CPU’s.
